1. Field of the Invention
This invention relates to an epoxy resin composition and a resin-sealed semiconductor device.
2. Description of the Related Art
Epoxy resin possesses excellent mechanical, electrical insulation, and moisture-proofing properties, and is widely used as a highly reliable insulating material in semiconductor devices, electronic parts, and in the sealing and impregnation of electrical parts. Regarding the sealing of semiconductor devices, in particular, the main tendency goes toward the sealing based on the application of resin, particularly epoxy resin which can be manufactured in larger quantities and at lower cost than in the hermetic sealing process involving the use of ceramic material or metals.
The type of properties which are most required of resin employed as semiconductor-sealing material are that the resin be highly corrosion-proof, so as to prevent the metal (particularly aluminium) applied on the surface of a semiconductor element from deteriorating through breakage resulting from corrosion; and that the resin have high resistance to thermal impact, in order to protect a metal wire connecting a semiconductor element to a frame from being broken by thermal shock. Recently, the high integration of a semiconductor element has made it necessary to be fine line pattern, to enlarge the semiconductor chip, to decrease the volume of the resin package and reduce its thickness. When such a thin miniaturized resin package (the so-called flat package) is applied on a printed circuit board, the package has to withstand a solder temperature of 260.degree. C. for 5 to 10 seconds. However, a flat package has a thin wall, both on the top and bottom walls of a semiconductor element. Therefore, when the flat package is dipped in molten solder kept at a temperature of 260.degree. C., this may give rise to cracks appearing in the resin constituting the package or the moisture-proofing properties of the resin may deteriorate. It has customarily been applied to decrease the internal stress of the resin, as a means for resolving the above-mentioned problem. To this end, natural rubber, for example, has been added to the epoxy resin. However, the resultant denatured resin has the defect in that its moisture-proofing properties are weakened.
The conventional epoxy resin composition has drawbacks in that it undergoes great internal stress. When, therefore, a large semiconductor chip is sealed in the prior art resin composition, the metal bonding wire is a resin-molded semiconductor device is broken; cracks may appear in the resin itself; dipping in the molten solder causes the resin to readily fall off the frame; and the moisture-proofing properties of the resin deteriorate.